In dynamic backlight modules, direct type light source structures are typically used. In a direct type light source structure, direct type light sources, such as light-emitting diodes (LEDs), are arranged in several regions under (or behind) a display panel. The direct type light source structure will dynamically display with the brightness according to the requirements of the displayed video frame; in other word, the light source structure's brightness is dynamically adjusted in different regions of the light source structure so that contrast ratio (maximum brightness to minimum brightness) can be improved. However, the direct type light source structure needs a relatively large number of light-emitting diodes and a relatively large light-mixing distance, so that the required thickness of the backlight module is increased. There are also light-mixing overlap bands between the regions, so that the contrast between the regions is poor.
FIG. 5 depicts a light-mixing space and light-mixing overlap in a conventional backlight module 500. Various LEDs 504 in a section of the backlight module 500 are arranged on a support structure 502, with the LEDs 504 in the depicted section separated into region I and region II. The LEDs 504 can include LEDs of different colors (such as red, green, and blue). Region I corresponds to a dim region of a displayed video frame (a dim region is a region of relatively low brightness), whereas region II corresponds to a bright region of the displayed video frame.
A color-mixing space 506 is provided between the LEDs 504 and a diffuser plate 508 to allow mixing of the different color light from the LEDs 504. The color-mixing space 506 also allows for brightness mixing. As noted above, a conventional backlight module requires that the light-mixing distance (thickness of the light-mixing space 506) be relatively large, which adds to the overall size of the backlight module 500.
Also, light from LEDs in the bright region (region II) can overlap into the dim region (region I) within the light-mixing space 506. This overlap results in a light-mixing overlap band 510, as depicted in FIG. 5, which can cause the brightness in the dim region (region I) to increase, thereby causing reduced contrast ratio between the bright and dim regions.
Furthermore, because the thickness of the backlight module composed of the direct type light source structure cannot be effectively reduced, some studies have been aimed at side-edge type light-mixing structures. The thickness of the backlight module composed of the conventional side-edge type light-mixing structure can be reduced; however, the light-mixing overlap phenomenon between regions still exists, and the contrast between the regions remains poor. Also, in a conventional side-edge type light mixing structure, a light guide plate with a complicated shape is needed, which increases manufacturing complexity and reduces product yield. Also, the possible range of the sizes of conventional side-edge type light mixing structures is limited, and for small liquid crystal display devices, the thickness of conventional side-edge type light mixing structures may still be too large. Furthermore, in this type of structure, the light sources are disposed on the side edge, so that the assembly and the dissipation of heat of the light sources become more complex, thereby increasing the fabrication difficulty of the module and reducing the product yield.